Predation, which is a fundamental force in ecosystems, has been found to decrease in intensity with elevation and latitude. The mechanisms behind this pattern, however, remain unaddressed. Using visual sampling of potential predators and live flies as baits, we assessed predation patterns along 4000-meter elevation transects on either side of the equatorial Andes. We found that at the lower elevations around eighty percent of predation events on our insect baits were due to ants. The decline in predation with elevation was mainly driven by a decline in the abundance of ants, whose importance relative to other predators also declined. We show that both predator density and activity (predation rate per individual predator) decreased with elevation, thus ascribing specific mechanisms to known predation patterns. We suggest that changes in these two mechanisms may reflect changes in primary productivity and metabolic rate with temperature, factors of potential relevance across latitudinal and other macroecological gradients, in particular for ectotherm predators and prey.